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My astronomy project:
2, Internal gearbox alternatives:
The internal spur gear box cause backlash and is not very smooth. I have got a lot of tips from forums what to do with this internal gearbox.
Almost all of them say: Replace it with a timing belt drive. And maybe that is a good solution, but a bolt on kit cost 180 Euro and this old mount is maybe not worth it, better to save the money to a new and better mount. I have looked at standard timing pulleys that doesn't cost very much. They will give another gear ratio and then the hand terminal doesn't work anymore. That doesn't concern me because I don't use the hand terminal, I control it from the computer with EQMOD and can change the gear ratio in the setup.
A list of the alternative I have:
1, Keep the spur gearbox:
This is how the internal gearbox looks disassembled.
The small gear has 12 teeth and the big 47 teeth. That gives a gear ratio of 47 / 12 = 3.9167. The middle gear doesn't change the gear ratio, only reverse the rotation and give some distance between the first and last gear. They are not equal between the RA and the DEC axis.
First I will try to get this gearbox to have less backlash and run more smooth. But it don't look very promising.
2, Replace it with a timing belt kit:
With this solution it is easy, just install the new timing belt kit.
There are at least two EQ6 time belt driving kits:
Both of them use a narrow 4 mm timing belt and a special 47 teeth timing pulley, that is what makes it expensive.
But it could be tricky to have the correct tension of the belt. The chassis of the EQ6 mount is very closed and then it's hard to see what's going on inside. See how this man solved it:
3, Replace it with a standard timing belt:
If I can use standard timing belts it will reduce the cost a lot. T2.5 pulleys has normally a 6 mm wide belt. But can I fit that belt in this small chassis?
The maximum width is about 9 mm with out doing any mechanical work on the chassis. To have some margin, maybe 8 mm width will fit.
The maximum width of the hub is about 15 mm.
The axis diameter is 12 mm. To lock the pulleys against the axis I need two lock screws.
The maximum diameter of the big pulley is 39 mm included the belt. A T2.5 48 teeth pulley has a diameter of 37.7 mm, maybe that will fit included the belt. A 60 teeth pulley has a diameter of 47.25 mm, but then there is some milling work to do. Four pulleys and two belt I can have for about 25 Euros, but needs some work to fit.
4, Replace it with a direct driven motor with an internal planetary gearbox:
An EQ6 mounts gear ration on the worm gear is only 180:1 and then it need another gearbox between the stepper motor and the worm gear. The built in gearbox is about 3.9:1. Together they give a total of 705:1 gear ratio.
Gear ratio data on Skywatcher's mounts:
With a gear ratio 360:1 and a 400 steps / revolution stepper motor you maybe can mount the stepper motor direct on the worm gear shaft. There are also DC servo motors that can be used, but I have no experience from that kind of motors yet.
I have no experience of small planetary gears. If it work I can set the stepper motor direct on the worm gear axis and then it should give a very good performance. One disadvantage is that the motors protrude outside the mount chassis.
Does it really exist a backlash free gearbox? General info about gear boxes:
It will look something like this but with stepper motors with a built in planetary gearbox:
With Nema17 motors I maybe can keep the EQ6 driver board. A gear ratio of 4:1 is safest to choose, close to the original.
Example of a stepper motor with built in planetary gearbox:
To install this motor you must have some holder and a shaft connector, from 8 mm to 12 mm. The DC resistance is 1.6 ohm, the EQ6 mounts original stepper motors has a DC resistance of about 7.5 ohm. What you need depends on which motor driver you decide to use.
This direct drive shaft solution feels most appealing to me, but should I spend it on the EQ6 mount or wait until I get something better to spend the time and money on?
5. Direct driven motor with no gearbox at all:
This is of course the optimal solution, no gearbox at all. I collect information about it here.